1915] Clark: Occurrence of Oligocene in the Contra Costa Hills 19 



species of which are generally considered to be especially good hor- 

 izon determiners, such as Agasoma, Molopophorus, Priscofusus, and 

 Turritella. 



The Oligocene fauna, as found at Pittsburg, Oregon, and Lincoln 

 Creek, Washington, is fairly well represented throughout the western 

 part of Washington and the northwestern part of Oregon. This fauna 

 is everywhere very distinct both from that of the Eocene and from 

 that of the typical Miocene. The following conclusions are based 

 upon a large number of localities in Oregon and Washington, from 

 which Mr. Martin obtained representative faunas of the Oligocene and 

 Miocene formations. 



Nearly half of the determinable species from the Agasoma gravi- 

 dum zone as known in Contra Costa County, California, are found in 

 the Astoria series, as recognized by Arnold and Hannibal in Oregon 

 and Washington, which includes the Pittsburg beds and the Lincoln 

 Formation referred to above. The following are some of the described 

 species which are common to the two. (Those species marked with an 

 asterisk are believed to be characteristic of the Oligocene.) 



Cardium lorenzanum Arnold "Agasoma acuminatum Martin and 



*Macrocallista mathewsonii (Gabb) Anderson 



v ' *Aneillaria fishi Gabb 



*Mvtilus mathewsonii (Gabb) ™ . , n , , , 



v ' "Bursa matnewsoni (Gabb) 



Panope estrellana (Conrad) r , , , , . /n s 



1 ^ ' Calyptraea excentrica (Gabb) 



Pecten peckhami Gabb ' . ~ , , 



1 Jncus pyrilormis Gabb 



Phaeoides acutilineatus (Conrad) , ', , . ,. ~ , , 



v "Molopophorus biplieatus Gabb 



Solen eurtus Conrad , , , , . nn 



"Molopophorus gabbi Uall 



*Tellina lorenzanum Arnold . . „ x , 



*Fusmus (Priseotusus) heeoxi 



Tellina oregonensis Conrad (Arnold) 



* Agasoma gravidum (Gabb) *Turritella porterensis Weaver 



Besides the species listed above, a number of new species have been 

 found which are common to the two horizons. Some of these are 

 Cardium, n. sp., Chione, n. sp., Pitaria, n. sp., Pecten, n. sp., Solen, 

 n. sp., Spisula, n. sp., Solen, n. sp. aff. parallelus Gabb, Natica, n. sp., 

 Turris, n. sp. A., Turris, n. sp. B., Dentalium, n. sp. 



Of the species which are common to the Agasoma gravidum zone 

 of Contra Costa County, California, and the Oligocene of Oregon and 

 Washington, Cardium lorenzanum,, Tellina lorenzanum, and Fusinus 

 heeoxi were first described from the San Lorenzo of the Santa Cruz 

 Quadrangle. Turritclla porterensis was described from the Porter beds 

 of Washington, which beds Arnold correlates with his San Lorenzo and 

 which are placed by Weaver in the Blakeley Formation. Molopophorus 

 gabbi was described by Dall from the Astoria beds of Oregon. 



